The present invention relates to a servo control system, particularly a power steering system for a motor vehicle.
A servo control system of the above described type which is known from German Published Unexamined Patent Application No. 1,093,224, is a power steering system for a motor vehicle. That system has flange elements that are an axial distance from one another and are arranged at two shaft parts that have the same axis and are rotatable relative to one another. One flange element, in a non-rotatable and axially non-slidable manner, is connected with one shaft part, while the other flange element is held at the other shaft part in a non-rotatable, but axially slidable manner. Spring bars are arranged between the flange elements at a radial distance from the axis of the shaft parts, the ends of these spring bars being fastened at the front sides of the flange elements facing one another. The longitudinal axes of the spring bars are aligned tangentially with respect to a helix enveloping the shaft parts. As soon as a relative rotation occurs between the shaft parts, the spring bars change their slope with respect to the shaft axis, so that the axial distance of the flange elements from one another is changed.
The circumferential edge of the slidable flange element engages into a groove of a control slide of a control valve unit with a stationary housing, this control slide being arranged in parallel to the longitudinal axes of the shaft parts. As a result, the control slide carries out the same stroke as the axially slidable flange element.
When steering is actuated by the turning of the steering wheel, the shaft parts will carry out a relative rotation against the resistance of the spring bars that depends on the steering resistance. These spring bars try to keep the shaft parts in a normal position relative to one another. The sliding of the slidable flange element that is caused by the relative rotation actuates the control side of the servo valve unit so that a motor operator that is controlled by the servo valve unit supports the respective desired steering operation with a force that depends on the extent of the shifting of the control slide.
A power steering system that is similar in principle is described in German Published Examined Patent Application No. 1,166,636. In that system, guide rods that are rigid elements are arranged between a flange element that is arranged at one shaft part in a non-rotatable and axially non-slidable way, and a flange element that is connected with the other shaft part in a non-rotatable, but axially slidable way, the ends of these guide rods in each case being hinged at the flange-type elements. The longitudinal axes of the guide rods, in turn, extend tangentially with respect to a helix enveloping the shaft parts. As a result, during a relative rotation between the shaft parts, the slidable flange element, in turn, is slid in the direction of the axis of the shaft parts. This axial stroke will then be transmitted to the control valve unit of the power steering system.
In the above-described known constructions, the slidable flange element carries out relatively small strokes when the two shafts parts rotate relative to one another. Corresponding to the small strokes of the slidable flange element, the control slide of the control valve unit also carries out relatively small strokes. This has the result that the opening cross-sections of the control valve unit controlled by the control slide must be dimensioned to be relatively small, if the control cross-sections, during the shifting of the control slide, are to change by a larger factor. However, this requires that the fluid system of the servo control system must work with a higher pressure in order to make possible the flow of larger amounts of fluid through the control cross-sections.
It is therefore an objective of the invention to provide a servo control system or a power steering system that, with relatively low constructive expenditures and comparatively small dimensions, makes possible large control strokes and thus large control cross-sections and has low energy requirements.
This and other objectives are achieved in the present invention by providing a servo control system having first shaft means connected to a controlling mechanism and second shaft means connected to control gear, this second shaft means being elastically coupled to the first shaft means. The system includes a motor operator connected to the control gear and which is movable forwards and backwards in response to pressure. A control slide variably connects the pressure source to the motor operator in response to the displacement of the control slide. A displaceable element is arranged on one of the shaft means and is screwably displaceable in response to relative rotation between the first and second shaft means. This displaceable element is operatively connected to the control slide and displaces the control slide in response to the relative rotation between the first and second shaft means.
The present invention is based on the recognition that the axially slidable part, because of its screwably displaceable arrangement on one shaft part, during relative rotations between the shaft parts and the connected axial shifting of the displaceable part, carries out an additional rotating motion which, in turn, causes a change of the axial stroke. In this embodiment, the extent of the axial stroke is increased if the connecting rod or rods are aligned tangentially with respect to a helix enveloping the shaft parts, the slope of this helix being opposed to the slope of the helix reflecting the screwable displaceability.
According to a preferred embodiment of the invention, it is provided that each connecting line going through the joints of the connecting rods, in axial view of the shaft parts, extends tangentially to the shaft axis. In top view, the connecting line extends onto a plane that is parallel with respect to the axis and contains the connecting line. In this plane, the connecting line extends sloped to the axis of the shaft at an angle of about 45.degree., when the shaft parts, by means of the spring unit, are held in their relative central position, in other words, are not rotated relative to one another to the right or to the left. On the basis of this arrangement, the extent of the axial stroke of the slidable part is determined only by the amount of the relative rotation between the shaft parts, and not by the direction of the relative rotation
It is also advantageously provided to arrange at the displaceable element a ring disk or circular disk with an edge that is concentric with respect to the axis of the shaft parts, this edge, in a form-fitting manner, is connected with the control slide or with a part connected with it for the adjustment of the axis direction of the shaft parts, for example, in that the control slide or the part connected with it reaches around the edge of the ring disk or circular disk on both its sides.
Instead, it is also contemplated to provide a ring groove at the displaceable element concentrically to the axis of the shaft parts, this ring groove, in a form-fitting manner, being correspondingly connected with the control slide or with a part connected with it, such that the control slide or the part connected with it engages in the ring groove. Therefore, in both cases, the control slide and the displaceable element are coupled with respect to the drive in a very simple way.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings